A simple dilute-and-shoot method for screening and simultaneous quantification of nicotine and alkaloid impurities in electronic cigarette refills (e-liquids) by UHPLC-DAD

The electronic cigarette (e-cigarette) has emerged as a popular alternative to the traditional hazardous tobacco cigarette. The substantial increase in e-cigarette use also urgently calls for controlling the quality of e-cigarette refill liquid products (e-liquids). Currently, the most important quality indicator of e-liquid products is the quantification of nicotine and its related impurities. Although different methods have been published to measure nicotine and impurity levels, the majority of them use a targeted LC-MS/MS approach. There is, however, a need for more robust quantification methods that are easy to implement in most control (industrial and governmental) laboratories. Therefore, in this study, a simple dilute-and-shoot UHPLC-DAD method has been developed and validated for the simultaneous quantification of nicotine and its alkaloid impurities in electronic cigarette refills. An optimal separation of the alkaloids was achieved in a runtime of 11 min. The method was successfully validated using the “total error” approach in accordance with the validation requirements of ISO-17025. During this validation, interference between the target components and a number of popular flavouring compounds such as vanillin, maltol, ethylacetate, etc. could be excluded. In addition, small changes to the column temperature, pH and molar concentration of the mobile phase buffer were deliberately introduced in order to assess the robustness of the method. Only a slightly different outcome between the newly developed UV-detection method and the targeted MS approach was found, due to the sensitivity of the different detection techniques. However, in the context of quality control of nicotine related impurities, for which the European Pharmacopoeia limits are currently applied, the sensitivity of the UHPLC-DAD method was found to be within the acceptable range. Despite the somewhat lower selectivity of the newly developed UV-detection technique versus a targeted LC-MS/MS approach, it may be concluded that this method is a suitable alternative for quality control purposes.